Determining directions, angles and lengths as locations is required in many fields of application, such as e.g. geodetic surveying and for industrial measurements. Developments in angle metrology have led, via mechanical read processes, to fully automated location measurements, in particular angle or path measurements according to the current prior art.
Known automated location determination apparatuses generally comprise a code carrier and a scanning apparatus. In the case of angle measurement apparatuses, so-called angle encoders, the code carrier is usually embodied rotatably about an axis relative to a scanning apparatus, wherein an angle location of the code carrier then constitutes the variable to be measured. By way of example, the code carrier can have a division or encoding for determining the position, wherein the encoding may be applied to a surface or lateral face of the code carrier.
For the purposes of automatically acquiring the location, the code carrier, which is movable relative to the scanning apparatus, is scanned by a read head by means of various techniques. Known scanning methods include electronic-magnetic, electronic and optoelectronic methods (i.e. inductively based, capacitively based and optically based).
By way of example, location determination apparatuses are used in coordinate measuring devices or coordinate measuring machines (CMM).
An optical detector of an angle encoder for reading an optically readable code carrier, as described in WO 2008/019835, is, for example, a photodetector, a CCD line array or a CCD area array. In general, the code carrier is embodied as a circular disk or as a circular ring and carries a position code, which can be acquired optically, along the circumference thereof, of which code a section is imaged on the detector.
As disclosed in e.g. WO 2007/051575, known angle measurement devices generally comprise a so-called circular arc and a scanning apparatus. The circular arc is embodied as code carrier and has a division or encoding for determining the position on the circle. The encoding is applied to a surface, i.e. a circle face or a lateral face, of the code carrier.
WO 2008/141817 discloses a location determination apparatus with a linear encoder and/or an angle encoder. The code carrier and scanning apparatus are arranged in such a way that relative movement in one degree of freedom, in particular a relative rotational movement or a relative longitudinal movement along one axis, is made possible between code carrier and scanning apparatus.
The known location determination apparatuses, in particular for coordinate measuring machines or geodetic surveying machines such as e.g. total stations, have very different advantages and disadvantages.
Known location encoders, such as linear encoders and angle encoders, are characterized by a high measurement accuracy for supplying relative (i.e. incremental) or absolute position determination data, but a relatively low measurement speed, for example of the order of between 1 Hz and 20 Hz, and, as a result thereof, relatively low possible reading speed. Designs with a comparatively increased possible measurement speed are relatively expensive, in particular due to the more complicated mechanics and electronics required for this.